diff --git a/docs/dev-notes/2026-04-15/relative_evalution_voting/plan.md b/docs/dev-notes/2026-04-15/relative_evalution_voting/plan.md
new file mode 100644
index 000000000..40eda90b0
--- /dev/null
+++ b/docs/dev-notes/2026-04-15/relative_evalution_voting/plan.md
@@ -0,0 +1,34 @@
+# 概要
+
+このタスクでは、投票（相対評価）の実装を行う。
+相対評価とは、既にグレードが確定している問題に対してもユーザーの投票が反映される仕組みである。
+
+# 仕組み
+
+まず、ユーザーが投票したグレードから中央値を取得する。この処理はすでに実装済みである。
+
+そして、中央値グレードと確定しているグレードの差を求める。
+差は `gradeOrder(中央値) − gradeOrder(確定グレード)` で計算する（Q11=1, ..., D6=17）。
+正値はユーザーが確定グレードより難しいと感じていることを意味し、負値は簡単と感じていることを意味する。
+
+投票数が最小閾値（`MIN_VOTES_FOR_STATISTICS`）未満の場合は中央値が算出されないため、バッジは表示しない。
+
+差に応じて、以下のように5段階評価を行う。
+
+- 差が-2以下: --
+- 差が-1: -
+- 差が0: 何もなし（バッジ非表示）
+- 差が1: +
+- 差が2以上: ++
+
+グレードが未定のものに対しては、これまでと同様絶対評価を行う。
+
+# UI
+
+グレードが確定している問題のグレードアイコンの右上に「++」、「+」、「何もなし」、「-」、「--」の5段階評価を表示することで、確定したグレードからの体感難易度の乖離を表す。
+
+投票の際のUIは既存のものから変更しない。
+
+# 作業ブランチ
+
+`feature/relative_evaluation_voting`
diff --git a/src/features/votes/components/RelativeEvaluationBadge.svelte b/src/features/votes/components/RelativeEvaluationBadge.svelte
new file mode 100644
index 000000000..cefff7294
--- /dev/null
+++ b/src/features/votes/components/RelativeEvaluationBadge.svelte
@@ -0,0 +1,57 @@
+<script lang="ts">
+  import { Tooltip } from 'flowbite-svelte';
+
+  import type { TaskGrade } from '$lib/types/task';
+  import {
+    calcGradeDiff,
+    getRelativeEvaluationLabel,
+    getRelativeEvaluationTooltipText,
+  } from '$features/votes/utils/relative_evaluation';
+
+  interface Props {
+    officialGrade: TaskGrade;
+    medianGrade: TaskGrade;
+    /** Unique element ID used to anchor the Tooltip. Must be unique on the page. */
+    badgeId: string;
+    /**
+     * Set to false when the badge is rendered inside a `<button>`.
+     * The tooltip is suppressed and aria-hidden is applied since the
+     * parent button's sr-only text already covers screen reader needs.
+     * Default: true
+     */
+    showTooltip?: boolean;
+  }
+
+  let { officialGrade, medianGrade, badgeId, showTooltip = true }: Props = $props();
+
+  const label = $derived(getRelativeEvaluationLabel(calcGradeDiff(officialGrade, medianGrade)));
+  const isHarder = $derived(label.startsWith('+'));
+
+  const tooltipText = $derived(getRelativeEvaluationTooltipText(label));
+</script>
+
+{#if label}
+  <span
+    id={badgeId}
+    class="absolute -top-2 -right-2 z-10 rounded-full px-1 py-px text-[0.65rem] font-bold leading-none shadow-sm
+      {isHarder
+      ? 'bg-orange-400 text-white dark:bg-orange-500 dark:text-white'
+      : 'bg-sky-400 text-white dark:bg-sky-500 dark:text-white'}"
+    aria-hidden={!showTooltip}
+    role={showTooltip ? 'img' : undefined}
+    aria-label={showTooltip ? tooltipText : undefined}
+  >
+    {#if label === '--'}
+      -&thinsp;-
+    {:else if label === '++'}
+      +&thinsp;+
+    {:else}
+      {label}
+    {/if}
+  </span>
+  {#if showTooltip && tooltipText}
+    <Tooltip triggeredBy="#{badgeId}" placement="top">
+      {tooltipText}
+    </Tooltip>
+  {/if}
+{/if}
diff --git a/src/features/votes/components/VotableGrade.svelte b/src/features/votes/components/VotableGrade.svelte
index 623692cd9..95fdf0eb2 100644
--- a/src/features/votes/components/VotableGrade.svelte
+++ b/src/features/votes/components/VotableGrade.svelte
@@ -1,5 +1,5 @@
 <script lang="ts">
-  import { tick } from 'svelte';
+  import { tick, untrack } from 'svelte';
   import { enhance } from '$app/forms';
   import { resolve } from '$app/paths';
 
@@ -17,10 +17,15 @@
 
   import { getTaskGradeLabel } from '$lib/utils/task';
   import { nonPendingGrades, resolveDisplayGrade } from '$features/votes/utils/grade_options';
+  import {
+    calcGradeDiff,
+    getRelativeEvaluationLabel,
+  } from '$features/votes/utils/relative_evaluation';
   import { SIGNUP_PAGE, LOGIN_PAGE, EDIT_PROFILE_PAGE } from '$lib/constants/navbar-links';
 
   import GradeLabel from '$lib/components/GradeLabel.svelte';
   import InputFieldWrapper from '$lib/components/InputFieldWrapper.svelte';
+  import RelativeEvaluationBadge from '$features/votes/components/RelativeEvaluationBadge.svelte';
 
   interface Props {
     taskResult: TaskResult;
@@ -52,6 +57,19 @@
     taskResult.grade === TaskGrade.PENDING && displayGrade !== TaskGrade.PENDING,
   );
 
+  // Track the latest median grade locally so the badge updates immediately after voting,
+  // even for confirmed-grade tasks (where displayGrade does not change on vote).
+  // Initialized from the prop; updated by the vote handler after fetchMedianVote.
+  let latestMedianGrade = $state<TaskGrade | null>(untrack(() => estimatedGrade ?? null));
+
+  // Relative evaluation badge label: shown only for confirmed grades with a known median.
+  const relativeEvaluationLabel = $derived.by(() => {
+    if (taskResult.grade === TaskGrade.PENDING || !latestMedianGrade) {
+      return '';
+    }
+    return getRelativeEvaluationLabel(calcGradeDiff(taskResult.grade, latestMedianGrade));
+  });
+
   let isOpening = $state(false);
   let votedGrade = $state<TaskGrade | null>(null);
   let voteAbortController: AbortController | null = null;
@@ -113,8 +131,12 @@
           const taskId = formData.get('taskId') as string;
           const medianGrade = await fetchMedianVote(taskId, signal);
 
-          if (medianGrade !== null && taskResult.grade === TaskGrade.PENDING) {
-            displayGrade = medianGrade;
+          if (medianGrade !== null) {
+            // Always update latestMedianGrade so the relative evaluation badge refreshes.
+            latestMedianGrade = medianGrade;
+            if (taskResult.grade === TaskGrade.PENDING) {
+              displayGrade = medianGrade;
+            }
           }
         })
         .catch((error) => {
@@ -156,11 +178,22 @@
     onclick={() => onTriggerClick()}
   >
     <span class="sr-only">
-      Voted grade: {getTaskGradeLabel(displayGrade)}{isProvisional ? ', provisional' : ''}
+      Voted grade: {getTaskGradeLabel(displayGrade)}{relativeEvaluationLabel
+        ? `, relative evaluation: ${relativeEvaluationLabel}`
+        : ''}{isProvisional ? ', provisional' : ''}
     </span>
 
     <GradeLabel taskGrade={displayGrade} defaultPadding={0.25} defaultWidth={6} reducedWidth={6} />
 
+    {#if taskResult.grade !== TaskGrade.PENDING && latestMedianGrade}
+      <RelativeEvaluationBadge
+        officialGrade={taskResult.grade}
+        medianGrade={latestMedianGrade}
+        badgeId="relative-eval-{componentId}"
+        showTooltip={false}
+      />
+    {/if}
+
     <!-- Overlay -->
     <span
       aria-hidden="true"
diff --git a/src/features/votes/utils/relative_evaluation.test.ts b/src/features/votes/utils/relative_evaluation.test.ts
new file mode 100644
index 000000000..39aa29085
--- /dev/null
+++ b/src/features/votes/utils/relative_evaluation.test.ts
@@ -0,0 +1,123 @@
+import { describe, expect, test } from 'vitest';
+
+import { TaskGrade } from '$lib/types/task';
+import {
+  calcGradeDiff,
+  getRelativeEvaluationLabel,
+  getRelativeEvaluationTooltipText,
+} from './relative_evaluation';
+
+describe('calcGradeDiff', () => {
+  test('returns 0 when official and median are the same grade', () => {
+    expect(calcGradeDiff(TaskGrade.Q5, TaskGrade.Q5)).toBe(0);
+  });
+
+  test('returns positive when median is harder than official', () => {
+    // Q5(order 7) vs D1(order 12): diff = 12 - 7 = 5
+    expect(calcGradeDiff(TaskGrade.Q5, TaskGrade.D1)).toBeGreaterThan(0);
+  });
+
+  test('returns negative when median is easier than official', () => {
+    // D1(order 12) vs Q5(order 7): diff = 7 - 12 = -5
+    expect(calcGradeDiff(TaskGrade.D1, TaskGrade.Q5)).toBeLessThan(0);
+  });
+
+  test('returns 1 for adjacent grade upward (Q3 -> Q2)', () => {
+    expect(calcGradeDiff(TaskGrade.Q3, TaskGrade.Q2)).toBe(1);
+  });
+
+  test('returns -1 for adjacent grade downward (Q2 -> Q3)', () => {
+    expect(calcGradeDiff(TaskGrade.Q2, TaskGrade.Q3)).toBe(-1);
+  });
+
+  test('returns 2 for two-step grade upward (Q3 -> Q1)', () => {
+    expect(calcGradeDiff(TaskGrade.Q3, TaskGrade.Q1)).toBe(2);
+  });
+
+  test('handles boundary grades Q11 and D6', () => {
+    // D6(17) - Q11(1) = 16
+    expect(calcGradeDiff(TaskGrade.Q11, TaskGrade.D6)).toBe(16);
+    // Q11(1) - D6(17) = -16
+    expect(calcGradeDiff(TaskGrade.D6, TaskGrade.Q11)).toBe(-16);
+  });
+
+  describe('D-tier grades', () => {
+    test('returns 0 when both are the same D grade', () => {
+      expect(calcGradeDiff(TaskGrade.D3, TaskGrade.D3)).toBe(0);
+    });
+
+    test('returns -1 for adjacent D grade downward (D3 -> D2)', () => {
+      expect(calcGradeDiff(TaskGrade.D3, TaskGrade.D2)).toBe(-1);
+    });
+
+    test('returns 1 for adjacent D grade upward (D2 -> D3)', () => {
+      expect(calcGradeDiff(TaskGrade.D2, TaskGrade.D3)).toBe(1);
+    });
+
+    test('returns -2 for two-step D grade downward (D4 -> D2)', () => {
+      expect(calcGradeDiff(TaskGrade.D4, TaskGrade.D2)).toBe(-2);
+    });
+
+    test('returns 2 for two-step D grade upward (D2 -> D4)', () => {
+      expect(calcGradeDiff(TaskGrade.D2, TaskGrade.D4)).toBe(2);
+    });
+  });
+
+  describe('Q1/D1 boundary', () => {
+    test('returns 1 when median crosses from Q1 to D1 (adjacent upward)', () => {
+      expect(calcGradeDiff(TaskGrade.Q1, TaskGrade.D1)).toBe(1);
+    });
+
+    test('returns -1 when median crosses from D1 to Q1 (adjacent downward)', () => {
+      expect(calcGradeDiff(TaskGrade.D1, TaskGrade.Q1)).toBe(-1);
+    });
+  });
+});
+
+describe('getRelativeEvaluationLabel', () => {
+  test('returns "++" for diff >= 2', () => {
+    expect(getRelativeEvaluationLabel(2)).toBe('++');
+    expect(getRelativeEvaluationLabel(5)).toBe('++');
+    expect(getRelativeEvaluationLabel(16)).toBe('++');
+  });
+
+  test('returns "+" for diff === 1', () => {
+    expect(getRelativeEvaluationLabel(1)).toBe('+');
+  });
+
+  test('returns "" for diff === 0', () => {
+    expect(getRelativeEvaluationLabel(0)).toBe('');
+  });
+
+  test('returns "-" for diff === -1', () => {
+    expect(getRelativeEvaluationLabel(-1)).toBe('-');
+  });
+
+  test('returns "--" for diff <= -2', () => {
+    expect(getRelativeEvaluationLabel(-2)).toBe('--');
+    expect(getRelativeEvaluationLabel(-5)).toBe('--');
+    expect(getRelativeEvaluationLabel(-16)).toBe('--');
+  });
+});
+
+describe('getRelativeEvaluationTooltipText', () => {
+  test('returns "" for empty string (default case)', () => {
+    expect(getRelativeEvaluationTooltipText('')).toBe('');
+  });
+
+  test('returns ++ for users feel the difficult than official grade', () => {
+    expect(getRelativeEvaluationTooltipText('++')).toBe('ユーザは「難しい」と評価');
+  });
+
+  test('returns + for users feel the slightly difficult than official grade', () => {
+    expect(getRelativeEvaluationTooltipText('+')).toBe('ユーザは「やや難しい」と評価');
+  });
+
+  test('returns - for users feel the slightly easy than official grade', () => {
+    expect(getRelativeEvaluationTooltipText('-')).toBe('ユーザは「やや易しい」と評価');
+  });
+
+  test('returns -- for users feel the easy than official grade', () => {
+    expect(getRelativeEvaluationTooltipText('--')).toBe('ユーザは「易しい」と評価');
+  });
+});
diff --git a/src/features/votes/utils/relative_evaluation.ts b/src/features/votes/utils/relative_evaluation.ts
new file mode 100644
index 000000000..5fd56c729
--- /dev/null
+++ b/src/features/votes/utils/relative_evaluation.ts
@@ -0,0 +1,65 @@
+import type { TaskGrade } from '$lib/types/task';
+import { getGradeOrder } from '$lib/utils/task';
+
+/**
+ * Computes the difference in grade order between the median vote and the official grade.
+ * Positive means users consider the problem harder than the official grade; negative means easier.
+ *
+ * @param officialGrade - The officially confirmed grade stored in the DB.
+ * @param medianGrade - The median grade derived from user votes.
+ * @returns `gradeOrder(medianGrade) - gradeOrder(officialGrade)`
+ */
+export function calcGradeDiff(officialGrade: TaskGrade, medianGrade: TaskGrade): number {
+  return getGradeOrder(medianGrade) - getGradeOrder(officialGrade);
+}
+
+/**
+ * Returns a Japanese tooltip string explaining the relative evaluation label.
+ *
+ * @param label - The label returned by {@link getRelativeEvaluationLabel}.
+ * @returns A human-readable explanation, or `''` when label is empty.
+ */
+export function getRelativeEvaluationTooltipText(label: string): string {
+  switch (label) {
+    case '++':
+      return 'ユーザは「難しい」と評価';
+    case '+':
+      return 'ユーザは「やや難しい」と評価';
+    case '-':
+      return 'ユーザは「やや易しい」と評価';
+    case '--':
+      return 'ユーザは「易しい」と評価';
+    default:
+      return '';
+  }
+}
+
+/**
+ * Converts a grade difference to a 5-level relative evaluation label.
+ *
+ * | diff   | label |
+ * | ------ | ----- |
+ * | ≤ −2   | `--`  |
+ * | −1     | `-`   |
+ * |  0     | `""`  |
+ * | +1     | `+`   |
+ * | ≥ +2   | `++`  |
+ *
+ * @param diff - The result of {@link calcGradeDiff}.
+ * @returns The display label string.
+ */
+export function getRelativeEvaluationLabel(diff: number): string {
+  if (diff <= -2) {
+    return '--';
+  }
+  if (diff === -1) {
+    return '-';
+  }
+  if (diff === 0) {
+    return '';
+  }
+  if (diff === 1) {
+    return '+';
+  }
+  return '++';
+}
diff --git a/src/routes/(admin)/vote_management/+page.svelte b/src/routes/(admin)/vote_management/+page.svelte
index 399426bc9..0b87519b7 100644
--- a/src/routes/(admin)/vote_management/+page.svelte
+++ b/src/routes/(admin)/vote_management/+page.svelte
@@ -12,8 +12,9 @@
 
   import HeadingOne from '$lib/components/HeadingOne.svelte';
   import GradeLabel from '$lib/components/GradeLabel.svelte';
+  import RelativeEvaluationBadge from '$features/votes/components/RelativeEvaluationBadge.svelte';
 
-  import { taskGradeValues } from '$lib/types/task';
+  import { taskGradeValues, TaskGrade } from '$lib/types/task';
   import { getTaskGradeLabel } from '$lib/utils/task';
 
   let { data } = $props();
@@ -47,20 +48,37 @@
           </TableBodyCell>
           <TableBodyCell class="text-sm">{stat.contestId}</TableBodyCell>
           <TableBodyCell>
-            <form method="POST" action="?/setTaskGrade" use:enhance>
-              <input type="hidden" name="taskId" value={stat.taskId} />
-              <select
-                name="grade"
-                onchange={(e) => (e.currentTarget as HTMLSelectElement).form?.requestSubmit()}
-                class="text-sm rounded-md border border-gray-300 dark:border-gray-600 bg-white dark:bg-gray-800 text-gray-700 dark:text-gray-300 px-2 py-1 focus:ring-primary-500 focus:border-primary-500 min-w-20"
-              >
-                {#each taskGradeValues as grade (grade)}
-                  <option value={grade} selected={stat.dbGrade === grade}>
-                    {grade === 'PENDING' ? '-' : getTaskGradeLabel(grade)}
-                  </option>
-                {/each}
-              </select>
-            </form>
+            <div class="flex items-center gap-2">
+              <form method="POST" action="?/setTaskGrade" use:enhance>
+                <input type="hidden" name="taskId" value={stat.taskId} />
+                <select
+                  name="grade"
+                  onchange={(e) => (e.currentTarget as HTMLSelectElement).form?.requestSubmit()}
+                  class="text-sm rounded-md border border-gray-300 dark:border-gray-600 bg-white dark:bg-gray-800 text-gray-700 dark:text-gray-300 px-2 py-1 focus:ring-primary-500 focus:border-primary-500 min-w-20"
+                >
+                  {#each taskGradeValues as grade (grade)}
+                    <option value={grade} selected={stat.dbGrade === grade}>
+                      {grade === 'PENDING' ? '-' : getTaskGradeLabel(grade)}
+                    </option>
+                  {/each}
+                </select>
+              </form>
+              {#if stat.dbGrade !== TaskGrade.PENDING && stat.estimatedGrade}
+                <div class="relative inline-block">
+                  <GradeLabel
+                    taskGrade={stat.dbGrade}
+                    defaultPadding={0.25}
+                    defaultWidth={6}
+                    reducedWidth={6}
+                  />
+                  <RelativeEvaluationBadge
+                    officialGrade={stat.dbGrade}
+                    medianGrade={stat.estimatedGrade}
+                    badgeId="relative-eval-{stat.taskId}"
+                  />
+                </div>
+              {/if}
+            </div>
           </TableBodyCell>
           <TableBodyCell>
             <GradeLabel
diff --git a/src/routes/votes/+page.svelte b/src/routes/votes/+page.svelte
index fd81136ed..28e5292be 100644
--- a/src/routes/votes/+page.svelte
+++ b/src/routes/votes/+page.svelte
@@ -15,6 +15,7 @@
 
   import HeadingOne from '$lib/components/HeadingOne.svelte';
   import GradeLabel from '$lib/components/GradeLabel.svelte';
+  import RelativeEvaluationBadge from '$features/votes/components/RelativeEvaluationBadge.svelte';
 
   import { TaskGrade } from '$lib/types/task';
 
@@ -78,7 +79,16 @@
                     </Tooltip>
                   {/if}
 
-                  <GradeLabel taskGrade={displayGrade} />
+                  <div class="relative inline-block">
+                    <GradeLabel taskGrade={displayGrade} />
+                    {#if task.grade !== TaskGrade.PENDING && task.estimatedGrade}
+                      <RelativeEvaluationBadge
+                        officialGrade={task.grade}
+                        medianGrade={task.estimatedGrade}
+                        badgeId="relative-eval-{task.task_id}"
+                      />
+                    {/if}
+                  </div>
                 </div>
               </TableBodyCell>
               <TableBodyCell class="text-base">
diff --git a/src/routes/votes/[slug]/+page.svelte b/src/routes/votes/[slug]/+page.svelte
index 79e24a8de..021bfa3d9 100644
--- a/src/routes/votes/[slug]/+page.svelte
+++ b/src/routes/votes/[slug]/+page.svelte
@@ -4,6 +4,7 @@
   import { Button, Tooltip } from 'flowbite-svelte';
   import FlaskConical from '@lucide/svelte/icons/flask-conical';
   import GradeLabel from '$lib/components/GradeLabel.svelte';
+  import RelativeEvaluationBadge from '$features/votes/components/RelativeEvaluationBadge.svelte';
 
   import { TaskGrade } from '$lib/types/task';
   import {
@@ -48,7 +49,16 @@
         {MIN_VOTES_FOR_STATISTICS}票以上集まると中央値が暫定グレードとして一覧表に反映されます。
       </Tooltip>
     {/if}
-    <GradeLabel taskGrade={displayGrade} />
+    <div class="relative inline-block">
+      <GradeLabel taskGrade={displayGrade} />
+      {#if data.task.grade !== TaskGrade.PENDING && data.stats?.grade}
+        <RelativeEvaluationBadge
+          officialGrade={data.task.grade}
+          medianGrade={data.stats.grade}
+          badgeId="relative-eval-{data.task.task_id}"
+        />
+      {/if}
+    </div>
     <h1 class="text-3xl font-normal truncate dark:text-white">
       <a
         href={getTaskUrl(data.task.contest_id, data.task.task_id)}